How to get original indexes back?

[vianamp]

Hi. Great job with alphashape!

I am doing alpha_shape = alphashape.alphashape(points, 5), where points is a Nx3 numpy array.

I found that if I do alpha_shape.exterior.coords.xy I can retrieve the coordinates of the points in the alpha shape contour. I was wondering whether there is a way to retrieve instead the original indexes relative to points.

Many thanks,

[CMcNaughty]

@vianamp your alpha_shape variable there is a Shapely polygon object. I'm not sure this is the sort of thing I'd expect alphashape (the package) to handle. Using some basic mapping, you could probably determine this yourself:

point_to_index = {tuple(point): idx for idx, point in enumerate(points)}
alpha_shape = alphashape.alphashape(points, 5)
indices = {point_to_index[point] for point in alpha_shape.exterior.coords}

where indices is a set of all your original points indexes in the alpha_shape exterior. Note that this probably isn't a sufficient solution as shapely's internal coords are always floats while I'm unsure your points array is necessarily all floats